Patent GB-569576-A (GB)
Title: Improvements in radio-receivers
IPC: H04B7/08
Filed: 1943-10-25
Abstract: 569,576. Wireless receiving systems. MARCONI'S WIRELESS TELEGRAPH CO., Ltd., and BEANLAND, C. P. Oct. 25, 1943, No. 17566. [Class 40 (v)] A diversity radio receiving system includes.a plurality of constituent receivers each of which embodies an automatic gain controlling system which includes an automatic gain load resistor to which the output of an automatic gain rectifier may be applied and from which automatic gain potentials are derived, in combination with a unit common to all the constituent receivers which includes an input load resistor to which the outputs from the automatic gain rectifiers of said receivers are transferred from said automatic gain load resistors and applied in common, a triode to which potentials from across said input load resistor are applied, and a diode having an output load resistor, said triode and diode being coupled by means of a common cathode resistor, potentials from said output load resistor being applied to the automatic gain load resistors of all the constituent receivers in common. The Figure shows an arrangement in which three receivers R1, R2, R3 are adapted either for separate operation with individual automatic gain control, or for combined operation in a diversity receiving system with a single automatic gain control arrangement which acts to suppress all but the strongest signal being received. In the receiver R1, the anode of the A.V.C. diode d is connected through a time-constant circuit tc to an external terminal 1t<1>, and one end of a load resistor lr is connected to a second external terminal 1t<11>. If terminals lt<1> and lt<11> are connected together, A.V.C. potentials developed across resistor lr are applied over leads if and hf to the I.F. and H.F. stages respectively of the receiver R1. Receivers R2 and R3 have similar arrangements and corresponding pairs of external terminals 2t<1>, 2t<11> and 3t<1>, 3t<11>. Switches S1, S2, S3 are provided for bridging the pairs of terminals when one or more of the receivers are to operate individually. For diversity reception, the switches S1 ... S3 are opened and terminals lt<1> ... 3t<1> are connected together and to the grid of a double-diode-triode dt. An input resistor ir is provided having a value so as to give a small time constant. The anode of the triode section is given a positive potential while the cathode is connected to a point at a considerable negative potential by a resistance kr such as to make the cathode slightly positive when no voltage is applied to the grid. The diode anodes ad are connected together and to one end of a potentiometer resistance pr having a tapping point connected to the terminals 1t<11> ... 3t<11>. With no signal, the triode section is passing current and the diode is cut off. When any of the diodes provides an A.V.C. voltage which is developed across ir, the current through the triode section is reduced and the cathode goes negative to cause the diode section to conduct. A negative potential corresponding to the largest of the A.V.C. potentials developed by receivers R1 ... R3 is taken from the tapping on pr and fed back to all of the receivers. This ensures that the signal utilised is that from the receiver having the strongest signal.